The present embodiments relate to medical imaging. In particular, multi-modal fused visualization of ultrasound imaging and nuclear medicine imaging are provided.
Diagnostic medical modalities, such as computed tomography (CT), magnetic resonance (MR), and ultrasound acquire detailed images. The images depict anatomical structures, such as location of internal organs and tumors. Other modalities, such as positron emission tomography (PET) and single positron emission computed tomography (SPECT), may visualize functional changes or information. PET and SPECT may show areas of cancerous growth or other operation of anatomy, but with less or no details about the surrounding anatomy.
Multi-modal fusion of anatomical and functional information is an effective way to provide greater distinction between physiological (e.g., organ) uptake and pathological (e.g., cancerous) uptake of a tracer. The multi-modal fusion may allow better diagnosis of cancerous masses, particularly in cases where the cancerous tissue is not well delineated in the anatomical images.
The process of fusing such information requires the overlapping images from different modalities to be visualized within a common coordinate system and overlaid or blended together. PET and CT may be combined into one device with know spatial relationship. For both 3D tomography scanning procedures, a patient lies on a motorized bed which moves inside a doughnut-shaped image acquisition device. Both types of images are acquired together in one scanning procedure.
If images are acquired using separate medical devices, calibration and tracking of the devices are used to provide a common coordinate space. Tracking devices (e.g., magnetic or optical sensors) and registration algorithms may be used to compute the proper correspondence between pixels in the respective images. Deformable registration may compensate for deformation and/or distortion and other anatomical changes that may have occurred if the images have been acquired at different times.
Multi-modality fusion based on tracked and registered images is typically a complex and time consuming procedure for the user. Some errors in the registration and tracking process may occur, producing misaligned results. Sometimes registration algorithms fail altogether, particularly when the images being registered together are of modalities that look so different from each other that matching features are difficult to identify.
The fusion of ultrasound with other modalities is challenging. Ultrasound images suffer from speckle noise artifacts and are not easily matched with higher quality images, such as CT or MR scans. For fusion of ultrasound with CT, ultrasound images are simulated from CT scans to find corresponding features in real ultrasound images. Such systems require two separate acquisition procedures to take place and require calibration of a tracking device attached to the ultrasound transducer probe as well as a registration algorithm to compute correspondence between a previously acquired CT scan and live ultrasound images. Such tracking is subject to registration errors.
The small form factor of hand-held transducer probes makes ultrasound an ideal imaging modality for interventional image-guided procedures. In addition to image generation, ultrasound may also be used for non-invasive therapeutic treatment. One ultrasound transducer for combined diagnostic and therapeutic use may be provided. Unfortunately there are still tumors and lesions that are not easily discernable in ultrasound images.
In nuclear medicine, hand-held nuclear activity devices, such as a gamma probe or a beta probe, are capable of detecting the uptake of injected tumor-seeking radiopharmaceuticals. Gamma probes, for example, are used in parathyroid and sentinel lymph node surgery, where the gamma probes provide an audible signal to locate regions where injected radionuclides are present. The locations detected with a gamma probe may be visualized rather than just relying on an audible signal. A tracking system measures the position of data acquired by the gamma probe to compute the images. Such images may then be fused with image data coming from other detectors. For example, images produced with an optically-tracked gamma probe are fused together with images from a video camera calibrated into the same coordinate space. The resulting fused image shows the location of sentinel lymph nodes overlaid onto the patient's skin, providing guidance to surgeons. However, optical tracking has the disadvantage of requiring an un-occluded view of the region of interest by the tracking camera and calibrated marker positions, and suffers from limited accuracy.
For fusing with ultrasound, separate tracking units ensure that the position and orientation of the separate ultrasound and gamma detectors are known. This combined multi-modal fusion of medical imaging data relies on tracking and registration of separate detectors held in place by two hands as part of a complex system requiring careful calibration, accurate tracking, and registration of images acquired by separate medical imaging devices.